Synchronous flowering times and asymmetrical hybridization in Typha latifolia and T-angustifolia in northeastern North America

Cattails (Typha spp.) in northeastern North American wetlands are increasingly dominant, partly because of hybridization between Typha latifolia and Typha angustifolia which results in the widespread and successful hybrid T. x glauca. Both parental species are protogynous, and previous studies have shown that T. angustifolia flowers earlier than T. latifolia. Nevertheless, experimental studies have shown that hybridization is overwhelmingly asymmetric, involving T. angustifolia female flowers and T. latifolia pollen which should have minimal overlap in the times at which they are produced. In this study we surveyed two Typha stands in eastern North America, and at both sites found substantial overlap in the times at which the parental species and the hybrids shed pollen and presumably are receptive to fertilization; this means that flowering time is not a prezygotic barrier to either the formation of hybrids or their subsequent back-crossing to parental species. Consistent with experimental studies, all hybrids had T. angustifolia as their maternal parent. Our results suggest that reproductive barriers between Typha spp. are evolving. (c) 2012 Elsevier B.V. All rights reserved.